Cytochrome reductase is a large membrane protein complex which comprises the middle section of the mitochondrial respiratory chain. In 1994 we improved the crystals and tested protein from different species. Rabbit reductase crystallized in the same hexagonal space group with significantly improved order. Porcine reductase crystallized in a new space group with poor order. Chicken reductase gave orthorhombic (P212121 ) crystals with markedly better order, diffracting to 3 w. Furthermore these crystals can be frozen with no loss of order after equilibrating with cryoprotectant solution. We have located heavy atom sites in a TAMM derivative of the crystal.